The effect of fertilization on the productivity of Trifolium repens – in mono as well as in mixed culture – has been investigated in detail under Dutch conditions as well as under conditions elsewhere. In view of the agricultural aspects of such investigations, special attention was paid in the mixed cultures to the increase or decrease of Trifolium repens in the sward. Hardly any of these studies were directed to the distribution of this species in the sod. As Trifolium repens spreads by stolons there is a tendency of growing in clumps. However, it may be interesting to see to what extent this aggregation is affected by other factors. In a grazing experiment with various fertilization treatments it was found that the distribution of Trifolium repens demonstrated obvious clumping. Visual observation suggested that this legume demonstrated more aggregation in the fertilized treatments than in the non-fertilized treatments. Preliminary frequency readings with units of varying size confirmed this suggestion. These observations gave rise to a more detailed study of the extent of aggregation in the various fertilization treatments with different methods. The results are presented in this paper.